Far Cry 3 won't launch.....help

[The Mechanic]

Hi, I have downloaded Far Cry 3 and whenever I try to launch it, the "Preparing to launch...." screen comes on for about a second then automatically closes. After trying this 2 or 3 times another screen comes up that says "game failed to start (app already running)". Ive tried a bunch of things, such as redownloading the game. When I verify the cache, it says 1 files failed to validate, then I restart steam, but that doesnt do anything. help.

[Highway]

make sure Uplay is running as well